• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.22 no.1
• /
• pp.11-14
• /
• 2012

The AlGaN layer has direct wide bandgaps ranging from 3.4 to 6.2 eV. Nowadays, it is becoming more important to fabricate optical devices in an UV region for the many applications. The high quality AlGaN layer is necessary to establish the UV optical devices. However, the growth of AlGaN layer on GaN layer is difficult due to the lattice mismatch and difference thermal expansion coefficient between GaN layer and AlGaN layer. In this paper, we attempted to grow the LED structure on GaN template by mixed-source HVPE method with multi-sliding boat system. We tried to find the optical and lattice transition of active layer by control the Al content in mixed-source. For the growth of epi layer, the HCl and $NH_3$ gas were flowed over the mixed-source and the carrier gas was $N_2$. The temperature of source zone and growth zone was stabled at 900 and $1090^{\circ}C$, respectively. After the growth, we performed the x-ray diffraction (XRD) and electro luminescence (EL) measurement.

• New Physics: Sae Mulli
• /
• v.68 no.12
• /
• pp.1281-1287
• /
• 2018

In this study, $Al_xGa_{1-x}N$ films were grown on (0001) sapphire substrates by using metal-organic chemical vapor deposition (MOCVD). The crystallinity of the grown films was examined with X-ray diffraction (XRD) patterns. The surfaces and the chemical properties of the $Al_xGa_{1-x}N$ films were investigated using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The optical properties of the $Al_xGa_{1-x}N$ film were studied in a wide photon energy range between 2.0 ~ 8.7 eV by using spectroscopic ellipsometry (SE) at room temperature. The data obtained by using SE were analyzed to find the critical points of the pseudodielectric function spectra, $<{\varepsilon}(E)>=<{\varepsilon}_1(E)>+i<{\varepsilon}_2(E)>$. In addition, the second derivative spectra, $d^2<{\varepsilon}(E)>/dE^2$, of the pseudodielectric function for the $Al_xGa_{1-x}N$ films were numerically calculated to determine the critical points (CPs), such as the $E_0$, $E_1$, and $E_2$ structure. For the four samples (x = 0.18, 0.21, 0.25, 0.29) between a composition of x = 0.18 and x = 0.29, changes in the critical points (blue-shifts) with increasing Al composition at 300 K for the $Al_xGa_{1-x}N$ film were observed via ellipsometric measurements for the first time.

• Cement Symposium
• /
• s.36
• /
• pp.38-46
• /
• 2009

• Proceedings of the Materials Research Society of Korea Conference
• /
• 1994.11a
• /
• pp.98-98
• /
• 1994

최근 청색반도체레이저의 실현을 위하여 ZnSe가 대표하는 II-Ⅵ족 화합물반도체와 Gan가 대표하는 III족 질화물반도체분야에서 집중적인 연구가 이루어지고 있으며, 아직까지 실용화 되지 않고 있는 청색반도체레이저의 출현에 대하여 많은관심이 모아지고 있다. III족 질화물반도체는 InM(Eg:1.9eV)부터 AIN(Eg: 6.2eV)에 이르기까지 전 조성영역에서 완전한 고용체를 이루며, 실온에서 직접천이형 에너지 대구조를 가지므로 청색 혹은 자외영역에서 동작하는 발광소자를 제작하는데 있어 유망시 되고 있는 소재이다. 특히 GaN와 InN의 3원흔정인 GaInN를 활성층으로 이용하면 그 발전파장을 370nm부터 650nm까지 즉 가시 전 영역으로부터 근 자외영역을 포함할 수 있게 된다. 이 연구에서는 AIGaN/GaInN 이중이종접합(DH) 구조의 고아여기에 의한 유도방출고아의 편광 특성을 조사하였다. 유기금속기상에피텍셜(MOVPE)법으로 성장한 AIGaN/GaInN DH 구조의 표면에 수직으로 펄스 발진 질소레이저(파장: 337.1cm, 주기 10Hz, 폭: 8nsec) 빔을 조사하고 DH구조의 단면으로부터의 유도방출광을 편광기를 통과 시킨 후 스펙트럼을 측정하였다. 입사고아 밀도가 증가함에 따라 약 402nm의 파장에서 유도발출에 의한 가도가 큰 피크가 나타났고, 그 반치폭은 약 18meV이었다. 실온에서 AIGaN/GaInN DH 구조로 부터의 유도방출에 필요한 입사광밀도의 임계치는 약 130㎾/$\textrm{cm}^2$이었다. 한편 편광각이 90$^{\circ}$일때는 발광스펙트럼의 강도가 매우 낮고 단지 자연방출에 의한 스펙트럼만이 나타났다. 편광각이 0$^{\circ}$일 때 최대의 방출광 강도를 나타내었으며, 편광각이 -90$^{\circ}$로 회전함에 따라 발고아강도의 강도가 감소하였다. 이와 같은 결과는 광여기에 의하여 AIGaN/GaInN DH 로 부터의 유도방출광이 GaInN활성층의 단면에 평행한 전기장의방향으로, 즉 TE모드로 선형적으로 편광됨을 의미한다. AIGaN/GanN DH 로 부터의 유도방출이 선형적으로 TE모드로 편광되는 것은 이 구조를 이용한 청색 및 자외선 반도체 레이저다이오드의 실현에 매우 유익한 것이다.

• Korean Journal of Agricultural Science
• /
• v.43 no.1
• /
• pp.28-32
• /
• 2016

This experiment was carried out to determine optimal culture conditions for the production of cut flowers and tubers of Calla (Zantedeschia 'Black Magic') in highlands. To achieve the research purpose, growth of 'Black Magic' Calla influenced by tuber hardness (3.3 and $6.0kg/cm^2$), $GA_3$ concentration (0, 100 and $200mgL^{-1}$), duration of $GA_3$ treatment (24 hr, 12 hr and 30min before planting) were investigated. When tubers have high hardness, those were not severely injured by soft rot disease regardless of $GA_3$ concentrations and treatment durations. Tubers with low tuber hardness showed more than 90% of soft rot occurrence when treated with $200mgL^{-1}$ $GA_3$ for 24 hrs before planting. However, soft rot did not occur when tubers were treated with $200mgL^{-1}$ $GA_3$ for 12 hrs before planting. In conclusion, $GA_3$ treatment results showed soft rot occurrence statistically significant degree in accordance with the bulbs hardness. In addition, the yield of the cut flowers is the result received the greatest effect in accordance with the bulbs in size and appeared to not be determined in accordance with the $GA_3$ treatment concentration and hardness bulbs. To obtain flowers without soft rot symptom, tubers (as $6.0kg/cm^2$) should be completely dried after $GA_3$ treatment.

• Korean Journal of Materials Research
• /
• v.22 no.4
• /
• pp.185-189
• /
• 2012

We report plasma-assisted molecular beam epitaxy of $In_XGa_{1-X}N$ films on c-plane sapphire substrates. Prior to the growth of $In_XGa_{1-X}N$ films, GaN film was grown on the nitride c-plane sapphire substrate by two-dimensional (2D) growth mode. For the growth of GaN, Ga flux of $3.7{\times}10^{-8}$ torr as a beam equivalent pressure (BEP) and a plasma power of 150 W with a nitrogen flow rate of 0.76 sccm were fixed. The growth of 2D GaN growth was confirmed by $in-situ$ reflection high-energy electron diffraction (RHEED) by observing a streaky RHEED pattern with a strong specular spot. InN films showed lower growth rates even with the same growth conditions (same growth temperature, same plasma condition, and same BEP value of III element) than those of GaN films. It was observed that the growth rate of GaN is 1.7 times higher than that of InN, which is probably caused by the higher vapor pressure of In. For the growth of $In_xGa_{1-x}N$ films with different In compositions, total III-element flux (Ga plus In BEPs) was set to $3.7{\times}10^{-8}$ torr, which was the BEP value for the 2D growth of GaN. The In compositions of the $In_xGa_{1-x}N$ films were determined to be 28, 41, 45, and 53% based on the peak position of (0002) reflection in x-ray ${\theta}-2{\theta}$ measurements. The growth of $In_xGa_{1-x}N$ films did not show a streaky RHEED pattern but showed spotty patterns with weak streaky lines. This means that the net sticking coefficients of In and Ga, considered based on the growth rates of GaN and InN, are not the only factor governing the growth mode; another factor such as migration velocity should be considered. The sample with an In composition of 41% showed the lowest full width at half maximum value of 0.20 degree from the x-ray (0002) omega rocking curve measurements and the lowest root mean square roughness value of 0.71 nm.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.376-376
• /
• 2011

I-III-VI2 chalcopyrite compounds, particularly copper, indium, gallium selenide(Cu(InxGa1-x)Se2, CIGS), are effective light-absorbing materials in thin-film solar application. They are direct band-gap semiconductors with correspondingly high optical absorption coefficients. Also they are stable under long-term excitation. CIS (CIGS) solar cell reached conversion efficiencies as high as 19.5%. Several methods to prepare CIS (CIGS) absorber films have been reported, such as co-evaporation, sputtering, selenization, and electrodeposition. Until now, co-evaporation is the most successful technique for the preparation of CIS (CIGS) in terms of solar efficiency, but it seems difficult to scale up. CIS solar cells have been hindered by high costs associated with a fabrication process. Therefore, inorganic colloidal ink suitable for a scalable coating process could be a key step in the development of low-cost solar cells. Here, we will present the preparation of CIS photo absorption layer by a solution process using novel metal precursors. Chalcopyrite copper indium diselenide (CuInSe2) nanocrystals ranging from 5 to 20nm in diameter were synthesized by arrested precipitation in solution. For the fabrication of CIS photo absorption layer, the CuInSe2 colloidal ink was prepared by dispersing in organic solvent and used to drop-casting on molybdenum substrate. We have characterized the nanoparticless and CIS layer by XRD, SEM, TEM, and ICP.

• Current Photovoltaic Research
• /
• v.6 no.2
• /
• pp.56-61
• /
• 2018

In this study, CIGS absorber layers were deposited on low-alkali glass and sodalime glass substrates and potasium floride (KF) of various thicknesses was supplied at an elevated temperature after the CIGS growth. The effect of KF post-deposition treatment on the two types of substrates was extremely different. On the low-alkali substrate, the open-circuit voltage (Voc) was improved but the fill-factor (FF) degradation was severe, whereas the sodalime substrate showed Voc deterioration and FF improvement. In the case of supplying 20 nm of KF on both substrates, the efficiency gain of 0.3~1.1%p was obtained. With increasing the KF thickness, a small protrusion-like microstructure developed on the surface of the absorber layer, and the microstructures that were not removed in the subsequent process were found to be the main cause of the FF loss.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.456.2-456.2
• /
• 2014

Cu(In,Ga)Se2 (CIGS) 화합물은 태양광을 흡수하기에 가장 이상적인 약 1.04 eV의 에너지 금지대 폭과 높은 광흡수계수를 가지고 있으며, $450{\sim}590^{\circ}C$의 고온 공정에도 매우 안정하여 열 경화현상을 거의 보이지 않으므로 박막 태양전지로서 커다란 응용 잠재력을 갖고 있는 광흡수층 재료이다. CIGS 화합물 박막 태양전지의 효율은 연구실에서는 ~20%의 높은 효율을 보고하고 있으며, 모듈급에서도 ~13%의 효율을 보이고 있다. 그러나 CIGS 박막 태양전지를 대면적 또는 양산화에 적용하기 위해서는 20년 이상의 장기적인 수명을 보장할 수 있는 내구성을 갖추어야 한다. 본 연구에서는 CIGS 모듈의 장기적인 신뢰성을 평가하기 위해 CIGS PV 모듈을 대상으로 IEC-61646 규격을 이용하여 고온고습 시험 ($85^{\circ}C$/85% RH, 1000 h) 과 열충격 시험 ($-40^{\circ}C/140^{\circ}C$, 1000 cycles) 이 수행되었고, 두 종류의 가속 스트레스 시험 후에 모듈의 성능 저하에 영향을 미치는 요인들이 연구되었다. 또한, 모듈의 효율 저하의 원인을 규명하기 위해 투명전극 Al-doped ZnO (AZO)와 광흡수층 CIGS를 대상으로 고장분석을 수행하였다. AZO층과 CIGS층의 전기적 특성 분석, 결장상 분석 및 XPS 분석들을 종합하여 CIGS PV 모듈의 성능저하의 원인을 규명하였다.

• 한국신재생에너지학회:학술대회논문집
• /
• 2006.06a
• /
• pp.149-151
• /
• 2006

Cu계 $I-III-VI_2$화합물은 직접천이형 반도체로 광흡수계수가 매우 높아 박막형 태양전지 제조에 매우 유리하다. 또한 화학적으로 안정하며 Ga, Al 등을 첨가하면 에너지 금지대폭을 조절할 수 있어 Wide Bandgap 태양전지 및 탠덤구조 태양전지를 제조하기에도 용이하다 $CulnSe_2(CIS)$ 물질에서 In을 20-30% 정도 치환한 $Cu(In,Ga)Se_2(CIGS)$ 태양전지의 경우 19.5%의 세계 최고 효율을 보고하고 있으며 이는 다결정 실리콘 태양전지의 효율과 비슷한 수준이다. 본 연구에서는 동시 진공증발법을 이용하여 증착한 CIGS 박막을 이용하여 태양전지를 제조하였다. 공정의 재현성 및 결정립계가 큰 광흡수층 제조를 위하여 실시간 기판온도 모니터링 시스템을 도입하였으며 버퍼충으로는 용액성장한 CdS 박막을 사용하였다. SLG/MO/CIGS(CGS)/CdS/ZnO/Al 구조의 태양전지를 제조하여 면적 $0.5cm^2$에서 각각 17.5%의 효율을 얻었다.